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.TH PTHREAD_ATTR_GETGUARDSIZE 3C "Mar 23, 2005"
.SH NAME
pthread_attr_getguardsize, pthread_attr_setguardsize \- get or set thread
guardsize attribute
.SH SYNOPSIS
.LP
.nf
cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ]
#include <pthread.h>

\fBint\fR \fBpthread_attr_getguardsize\fR(\fBconst pthread_attr_t *restrict\fR \fIattr\fR,
     \fBsize_t *restrict\fR \fIguardsize\fR);
.fi

.LP
.nf
\fBint\fR \fBpthread_attr_setguardsize\fR(\fBpthread_attr_t *\fR\fIattr\fR, \fBsize_t\fR \fIguardsize\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fIguardsize\fR attribute controls the size of the guard area for the
created thread's stack. The \fIguardsize\fR attribute provides protection
against overflow of the stack pointer. If a thread's stack is created with
guard protection, the implementation allocates extra memory at the overflow end
of the stack as a buffer against stack overflow of the stack pointer. If an
application overflows into this buffer an error results (possibly in a
\fBSIGSEGV\fR signal being delivered to the thread).
.sp
.LP
The \fIguardsize\fR attribute is provided to the application for two reasons:
.RS +4
.TP
1.
Overflow protection can potentially result in wasted system resources. An
application that creates a large number of threads, and which knows its threads
will never overflow their stack, can save system resources by turning off guard
areas.
.RE
.RS +4
.TP
2.
When threads allocate large data structures on the stack, large guard areas
may be needed to detect stack overflow.
.RE
.sp
.LP
The  \fBpthread_attr_getguardsize()\fR function gets the \fIguardsize\fR
attribute in the \fIattr\fR object. This attribute is returned in the
\fIguardsize\fR parameter.
.sp
.LP
The  \fBpthread_attr_setguardsize()\fR function sets the \fIguardsize\fR
attribute in the \fIattr\fR object. The new value of this attribute is obtained
from the \fIguardsize\fR parameter. If \fIguardsize\fR is  \fB0\fR, a guard
area will not be provided for threads created with \fIattr\fR. If
\fIguardsize\fR is greater than  \fB0\fR, a guard area of at least size
\fIguardsize\fR bytes is provided for each thread created with \fIattr\fR.
.sp
.LP
A conforming implementation is permitted to round up the value contained in
\fIguardsize\fR to a multiple of the configurable system variable
\fBPAGESIZE.\fR If an implementation rounds up the value of \fIguardsize\fR to
a multiple of  \fBPAGESIZE,\fR a call to \fBpthread_attr_getguardsize()\fR
specifying \fIattr\fR will store in the \fIguardsize\fR parameter the guard
size specified by the previous  \fBpthread_attr_setguardsize()\fR function
call.
.sp
.LP
The default value of the \fIguardsize\fR attribute is  \fBPAGESIZE\fR bytes.
The actual value of  \fBPAGESIZE\fR is implementation-dependent and may not be
the same on all implementations.
.sp
.LP
If the \fIstackaddr\fR attribute has been set (that is, the caller is
allocating and managing its own thread stacks), the \fIguardsize\fR attribute
is ignored and no protection will be provided by the implementation. It is the
responsibility of the application to manage stack overflow along with stack
allocation and management in this case.
.SH RETURN VALUES
.sp
.LP
If successful, the  \fBpthread_attr_getguardsize()\fR and
\fBpthread_attr_setguardsize()\fR functions return  \fB0\fR. Otherwise, an
error number is returned to indicate the error.
.SH ERRORS
.sp
.LP
The \fBpthread_attr_getguardsize()\fR and \fBpthread_attr_setguardsize()\fR
functions will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR \fR
.ad
.RS 11n
The attribute \fIattr\fR is invalid.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR \fR
.ad
.RS 11n
The parameter \fIguardsize\fR is invalid.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR \fR
.ad
.RS 11n
The parameter \fIguardsize\fR contains an invalid value.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR pthread_attr_init (3C),
.BR sysconf (3C),
.BR attributes (7),
.BR standards (7)
